This invention relates to a signal selection circuit capable of automatically selecting an input in a device having digital and analog inputs for one and the same audio source device.
Recent developments in the digital technique has enabled realization of various digital audio source devices such as a CD (Compact Disc Digital Audio System) player, a DAT (digital audio tape recorder) and a VDP (video disc player). Types of output signals of these digital audio devices differ from one another including a type in which an analog signal is produced after performing digital-to-analog conversion of the signal in the source device, one in which a digital signal is directly produced without digital-to-analog conversion and one in which an analog signal and a digital signal are produced in parallel.
Accordingly, the signal channel in a device such as a control amplifier to which the digital source device is connected differs depending upon whether the input signal applied from the digital source device to the device is an analog input or a digital input, i.e., if the connected device performs a digital signal processing, an analog signal is subjected to analog-to-digital conversion whereas if the connected device performs an analog signal processing, a digital signal is subject to digital-to-analog conversion. It is therefore necessary for the conncected devices to have both an analog input and a digital input for each digital source device so that they can cope with various types of output signals of the digital source device.
In a case where a listener connects a source device producing an analog signal and a digital signal in parallel to a device connected to this source device having two input terminals for one and the same digital source device or in a case where a listener connects a source device of an analog signal output type and a source device of a digital signal output type for the same type of source to the two input terminals of the connected device, it is necessary that signal selection means be provided between the two input terminals so as to prevent mixing of signals applied to the two input terminals.
In prior art devices, a switch is provided on the side of the device connected to a source device for selection of the signal and selection of the signal is left to manual operation of the listener.
In this prior art signal selection system, the listener is obliged to make two selections which are both troublesome and liable to cause mistakes, namely (1) which of the analog and digital signals should be selected (2) which source device should be selected.
It is an object of the invention to provide a signal selection circuit capable of automatically performing the signal selection.